The present invention broadly relates to an apparatus for shaping workpieces and, more specifically, pertains to a new and improved construction of an apparatus for shaping electrode workpieces by means of an abrading medium introduced into a gap between the latter and an abrading die member and inducing relative motion between the two.
Generally speaking, the present invention relates to an improved apparatus for shaping an electrode workpiece to a prescribed spatial configuration by means of an abrading die having the same spatial configuration but (slightly) different dimensions. The difference in dimensions leaves an abrading gap between the die and the workpiece into which an abrading medium is introduced. The apparatus induces relative motion of a first type between the die and the workpiece to generate or refine a desired spatial configuration of the electrode workpiece. Relative motion of this first type is a composite motion composed of a feed motion and a planetary or orbital motion. A motion of a second type is provided which induces retracting and advancing motions between the die and the workpiece in order to improve flushing conditions in the abrading gap.
Representative constructions of electrode shaping apparatuses are exemplified by U.S. Pat. No. 4,186,527, granted Feb. 5, 1980, U.S. Pat. No. 4,227,915, granted July 14, 1981 and U.S. Reissue Pat. No. 27,588, granted Feb. 27, 1973.
Die making encompasses the manufacture of dies, molds and forms for the pressure casting, injection molding, punching, hot forming, cold forming and forging of plastics, rubbers and metals, especially steel, as well as their respective mixtures and alloys. These dies are often complicated and of (pronounced) three-dimensional design. There is particular demand in the aircraft and automotive industries for such difficult to make forms, often in conjunction with the maintenance of very close tolerances. Workpiece or machine components (for instance in engine manufacture) of hard to machine materials (for instance high temperature resistant alloys) are also produced by processes employed in die making. Such dies or components are often produced by spark erosion or electro-chemical apparatus. The electrodes employed in this apparatus have the same complex surfaces as do the dies or components they produce. Recent technology employs special apparatus to manufacture such electrodes. The electrode is shaped from a blank of material by an abrading or grinding or filing process. The material may be for instance graphite. The tool, for instance abrading die required for this operation has the (negative) spatial configuration of the electrode with a small negative deviation from the nominal spatial configuration. The abrading or filing process is effected by providing a relative motion between the die and the material blank of the workpiece. An abrading medium is impregnated into the surface of the die to promote the abrading or filing action. In addition, a fluid is introduced into the abrading gap between the die and the workpiece.
The relative motion is composed of two types of motion components. One type is the feed motion of the abrading or filing die towards or away from the workpiece (vertical). This feed motion can also be circular (in a vertical plane). The other type is a revolving or circular motion of the electrode workpiece in a horizontal plane. The revolving motion is also called orbital or planetary. It can also be spherical. The radius or the eccentricity of the revolving motion can be adjustable.
The abrading process is continued until the electrode workpiece has assumed the spatial configuration of the abrading die. The process is then terminated. This is effected by setting a depth stop on the apparatus to the desired dimension. The spatial configuration of the electrode workpiece can be increased or reduced in size in relation to the spatial configuration of the die. This is effected by adjusting the eccentricity of the revolving motion. This known method of shaping the spatial configuration of an electrode workpiece has the following disadvantages:
(a) The eccentricity of the relative motion cannot be changed during the abrading process. The apparatus must be shut down to perform this operation.
(b) The pressure between the die and the electrode workpiece must be adapted to changing work conditions during the abrading process. The conditions of the abrading process vary in accordance with the size of the surface engaged in abrading between the die and the electrode workpiece. The size or angular orientation of the surface engaged in the abrading process can change within short periods of time. A corresponding adaptation of the abrading pressure to the abrading conditions and to the strength of the die and of the workpiece is not possible with known means of manufacture. Therefore, there is a risk that the abrading pressure is too high or too low at certain times. This results in either faultily finished surface regions or in damage to the die or to the electrode workpiece or in an excessive long abrading time. In any event, the manufacturing costs are unnecessarily increased.
(c) For improved flushing of the abrading gap, the die is periodically retracted from the workpiece and after a short interval advanced to the workpiece again. The flushing fluid transports abraded material out of the gap. The speed of the brief retraction and of the advance is greater than the speed of feeding during abrading or filing. As the die progresses more deeply into the material blank of the workpiece, the amount of surface area engaged in the abrading or filing process increases. The spatial configuration of the surface also becomes more complex. In both cases, the speed of retraction and advance is no longer adapted to the conditions in the abrading gap. This can lead to damage to the surfaces of the die and of the workpiece.
(d) The retraction and advance of the die is often effected with a greater force than necessary, since the force cannot be correlated to the mass or weight of the die, which varies from die to die. Each change in direction of motion and each acceleration or deceleration of the motion imparts impulse forces to the die, which have an undesirable effect on the accuracy of its adjustment in relation to the workpiece. This results in a poor quality of the spatial configuration of the workpiece.